I'm not really sure what you're critizisng? This was a study done in the early 1990s looking at what would be the best way to build a sauna. This isn't a study

I'm not really sure what you're critizisng? This was a study done in the early 1990s looking at what would be the best way to build a sauna. This isn't a study in HVAC optimization for a house. FWIW current finnish building code more-or-less require a heat exchanger in the exhaust air flow. It didn't in 1990.